Investigating the impact of sub-ice shelf melt on Antarctic ice sheet spin-up and projections

Abstract. Sub-ice shelf melting is critical for the stability of the Antarctic ice sheet, as it influences ice-shelf buttressing that reduces grounded ice flow. Previous studies have emphasized that uncertainties in the state of sub-ice shelf melting contribute to uncertainties in future sea-level projections. To better understand how sub-ice shelf melt rates affect model initialization and predictions, we adopt a single ice-sheet model (PISM) and investigate two different sub-ice shelf melt rate schemes during model spin-ups. We then drive the Antarctic ice sheet into the future using identical environmental forcings. We find that, despite closely matched steady-state geometries achieved through the spin-up process with different sub-ice shelf melt rates, the prognostic simulations reveal significantly divergent ice mass changes, particularly in marine ice sheet regions. By 2100, the difference in global sea-level contributions from the Antarctic ice sheet can be as large as ∼ 57 %, primarily from West Antarctica. This discrepancy arises because the spin-up initialization method alters the ice sheet's dynamic state, such as basal friction and thermal regimes, leading to differences in ice-sheet mass changes over time. Therefore, this study underscores the importance of sub-ice shelf melting and ice-sheet model initialization methods in reducing uncertainties in predicting the Antarctic ice sheet's future.